The normal onset of seasonal oestrous behaviour in Romney derived breeds can be advanced by the use of teaser rams and social facilitation. This technique was used, as part of a farm systems trial, to advance the start of lambing from September 1 to August 1. In the first year, the use of Dorset rams at ratios of 0, 3, 6 and 9 per 100 ewes resulted in 0, 72, 81 and 86% respectively of ewes ovulating at the silent oestrous. In the following year, a ratio of 8% was used in combination with CIDRs after the silent oestrous. This extra manipulation gave no advantage in terms of ewes lambing and ewes lambing multiples. Use of Coopworth rams instead of Dorsets and priming the teaser rams by exposure to oestrogen treated spayed ewes likewise had little impact. Over all years, teasing resulted in a similar proportion of ewes lambing (87%) compared to the later lambing non-teased groups (89%). However, the early groups had only 37% multiple births compared to the late lambing ewes (48%, P<0.01). The 31 day advance in start mate date in the early ewes resulted, on average, in a 27 day advance in mean lambing date (P<0.01). When weaned on the same date the early lambs were 2.27 kg heavier than the late lambs (P<0.01).
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 256-257, 1997
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